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base was completely submerged. The apparatus was now placed under 
a bell-jar with air, free from carbon dioxide, and the whole was 
exposed to the light. 
After some hours starch had been formed in this apparatus in 
Dahlia Yuarezit (exp. XXXIV) and in Populus pyramidalis (exp. 
XXXV); there was a strip of starch in the apical portion along the 
mercury, quite like that of the previous experiments; there was a 
similar strip in the basal portion under water, also along the edge 
of the mercury; and finally a narrow strip of starch had appeared 
in the mercury itself, at the place where the leaf had been in contact 
with the lower edge of the vertical glass plate and had therefore 
received light. 
The carbon dioxide, which in this case had been used up in starch- 
formation, could only have been derived from the portions of the 
leaf under the mereury and could scarcely be anything but carbon 
dioxide of respiration from these parts. 
When this had once become evident, a still simpler arrangement 
naturally suggested itself. For this purpose pieces of leaves, free 
from starch, were placed on a layer of mercury, were partially 
covered with black paper, and finally pressed under the mereury by 
means of a glass crystallising dish with flat bottom. The light could 
now reach those parts of the leaves which were not covered by 
black paper, through the bottom of the glass dish. 
Such experiments were made with Dahlia Yuarezi (exp. XXXVI, 
XXXVII and XLI), Sambucus nigra (exp. XXXVI), Syringa vul- 
garis (exp. XXXIX) and Tila platyphyllos (exp. XL). In all these 
experiments, which lasted about 5 hours, strips of starch were formed 
in the ordinary way at the border of the black paper in the lighted 
portions of the leaves; the border of the starch on the side opposite 
the paper was again sharply defined in many places by veins. 
We may hence assume, that in all the experiments of the second 
group, in which the result was negative, starch had been formed 
exclusively at the expense of the carbon dioxide, resulting from the 
respiration of the parts of the leaf under the mercury, which carbon 
dioxide had been transported a certain distance to those parts, which 
were exposed to light. 
In this case the supply of carbon dioxide from outside was 
prevented by the mercury, which also kept off the light. The re- 
spiratory carbon dioxide could therefore not be immediately reduced 
on the spot, but could spread and thus reach the lighted portions of 
the leaf in fairly large quantity. It should further be noted, that the 
epidermis of the darkened leaf-fragment was closed hermetically by 
